Silver is rallying the most among major commodities this year as about $9 trillion of debt tracked by the Bloomberg Global Developed Sovereign Bond Index offer yields below zero, meaning those who buy the debt and hold to maturity stand to lose money.

"That really changes the landscape," Chanin said in a telephone interview from New York this week. "If you have negative interest rates across sovereign debt, suddenly zero percent may start to look more attractive than negative rates. That's been causing more people to become interested in investing in precious metals."

Central banks around the world are cutting rates or engaging in massive asset purchases or both, sending yields on bonds from Japan to the U.K. to record lows. On Aug. 8, the Bank of England resumed gilt purchases while India's central bank Governor Raghuram Rajan said its policy stance remains accommodative.

Yields aren't the only driver. Silver is outperforming the quintessential haven, gold, because production of the white metal is forecast to decline for the first time since 2011 as physical demand is seen rising for a fourth straight year.

Output is set to fall 2.4% to 784.8 million ounces this year, researcher CPM Group said in report in June. Fabrication demand including jewelry, electronics and solar panels will rise 1.6% to 889.7 million ounces, it said. Secondary supply, including scrap and melted coins, will drop 1% to 203 million ounces, it said.

Silver — a byproduct in mines that produce zinc, lead, copper and gold — is rebounding after three straight annual losses that cut prices by more than half. The 2016 rally could be sustained, according to Fresnillo, the largest producer whose first-half profit more than doubled.

The rebound in silver prices is also spurring interest in companies that produce the metal, allowing PureFunds silver miner ETF to post the biggest return among over 6,000 ETFs tracked by Bloomberg that aren't leveraged. Its biggest holding, Coeur Mining, which explores and owns silver and gold mines, is up more than sixfold this year.

Coeur Mining's adjusted earnings in the second quarter reached 11 cents a share, topping the highest analyst estimate tracked by Bloomberg, as the company cut costs. The Chicago-based miner, which produces gold and silver, posted a first-quarter loss.

"We've seen investors seeking alternatives to traditional equities and traditional fixed income products," Todd Rosenbluth, a New York-based director of ETF research at S&P Global Market Intelligence, said by telephone Wednesday. Improvements in silver miners's operating efficiency and balance sheets "helped them become more profitable now that the prices have recovered."